While the Internet provides people with convenience, the Internet has also brought various risks. Some malicious users employ bots to improperly use Internet resources on a large scale. For example, some malicious users use automatic registering tools to batch register website accounts, inject meaningless characters, submit garbage data to servers, etc. Some malicious users waste server resources and affect the normal use of legitimate users. Also some malicious users continually access servers in an attempt to figure out the account passwords of legitimate users, thus these malicious users threaten the privacy and interests of legitimate users. Therefore, servers typically deploy techniques that can automatically distinguish between legitimate and malicious users and thereby reduce the risk of malicious use.
Verification codes are used to differentiate between legitimate and malicious users. Various methods for generating verification codes exist, such as verification by ASCII characters, questions and answers, and speech. Verification codes are generated by selecting the use of one of these types of methods on a server. However, with optical character recognition technology, automatic answering technology, and speech recognition technology, programs can increasingly submit correct verification codes automatically, and blocking malicious users has been increasingly difficult.